Fuel delivery: The ECM meters the fuel output of the injectors using pulse width signals. It varies the pulse width based on input signals. Inputs to the ECM include: air intake volume using the mass airflow sensor signal, ambient and coolant temperature signals, accelerator pedal signal, crankshaft and camshaft position signals, knock sensor signals.

Intake system (M54 engine): The resonance / turbulence intake system consists of two sets of three intake runners. Resonance valves are used to vary the length of the runners in order to enhance low end torque at low engine speeds or allow high volume air flow at medium or high engine speeds. The M54 intake is also equipped with a 5.5 mm turbulence port for each cylinder. These ports channel idle and low speed air from the idle speed control regulator to one intake valve in each cylinder. There are 2 intake valves per cylinder. Air rushing through one valve causes air swirl and more efficient fuel atomization in the cylinder.

Intake system (N52 engine): The Valvetronic system uses hardware and software to eliminate the conventional throttle mechanism. Instead of a throttle valve, intake air is regulated by adjusting valve lift. The engine is equipped with a Valvetronic actuator motor, which operates a cam gear, an eccentric shaft and intermediate levers to vary intake valve lift based on ECM signals. Similarly, the ECM controls idle speed by varying valve actuation. This engine is also equipped with 3-stage variable intake runners in a system known as DISA. DISA valves in the intake manifold are actuated by pulse-width modulated ECM signals.

Throttle control, idle control: In Z4 vehicles the throttle cable is eliminated and throttle actuation is completely electronic (drive-by-wire). In the M54 (6-cylinder) engine, the idle speed control valve is controlled by the ECM to bypass varying amounts of air around the closed throttle valve.

Ignition and knock control: The ignition system uses one ignition coil per cylinder (mounted under the engine cover), with each coil mounted above a spark plug. Multiple sparks per ignition cycle are used to reduce emissions and extend spark plug life. Spark timing is controlled by the ECM using an ignition spark "map". Spark timing is not adjustable. However, to prevent engine damage in case of adverse conditions or poor fuel quality, knock (detonation) sensors (green arrows) are mounted on the engine crankcase. These are microphones tuned to the frequency of engine knock and communicate such knock to the ECM. The ECM can respond to these signals by changing (usually retarding) ignition timing at one or more cylinders.

Exhaust manifolds and oxygen sensors: Oxygen sensor signals are used by the ECM to control fuel delivery. Z4 engines are equipped with two exhaust manifolds, each with an integrated catalytic converter. This allows the converters to heat up a very short time after a cold start. The manifolds are equipped with four oxygen sensors, one before each catalyst and one after.

Figure 1

Engine control module (ECM): The engine control module (ECM or DME) (red arrow) is mounted in the electronics-box (E-box) at the left rear of the engine compartment.

Ignition and knock control: The ignition system uses one ignition coil per cylinder (mounted under the engine cover - red arrow), with each coil mounted above a spark plug. Multiple sparks per ignition cycle are used to reduce emissions and extend spark plug life. Spark timing is controlled by the ECM using an ignition spark "map". Spark timing is not adjustable. However, to prevent engine damage in case of adverse conditions or poor fuel quality, knock (detonation) sensors (green arrows) are mounted on the engine crankcase. These are microphones tuned to the frequency of engine knock and communicate such knock to the ECM. The ECM can respond to these signals by changing (usually retarding) ignition timing at one or more cylinders.

Exhaust manifolds and oxygen sensors: Oxygen sensor signals are used by the ECM to control fuel delivery. Z4 engines are equipped with two exhaust manifolds, each with an integrated catalytic converter. This allows the converters to heat up a very short time after a cold start. The manifolds are equipped with four oxygen sensors, one before each catalyst and one after. The pre-catalyst sensors (B1S1, B2S1) are located in the exhaust manifold on the right side of the engine, just out of view. The red arrow points to the tip of B1S1. Post-catalyst sensors are located at the right rear of the engine (green arrow) just after the catalysts.

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